Our Astronomical Column

Abstract

THE PERIODICAL COMETS OF DE VICO AND BARNARD.—As was first pointed out by Prof. Weiss, there is a certain degree of resemblance between the elements of the comet discovered by Barnard in July, 1884, and those of the comet of short period detected by De Vico in August, 1844, which Leverrier considered was probably identical with the comet observed by Lahire at Paris in 1678, though not known to have been seen in the long intervening period. It appears from Brünnow's minute investigation of the orbit of De Vico's comet that the mean motion at perihelion passage in 1844 is not determinable from the observations within very narrow limits, as might rather have been expected, considering the degree of precision with which that comet was observed from the beginning of September to the end of December, Mr. Otto Struve's observations in particular being of remarkable excellence. According to Briinnow's later calculations, the results of which were published in his “Ann Arbor Notices,” the mean motion was close upon 650” daily, but he considered that it might be as small as 640” or as large as 660”, or, in other words, that the period of revolution at perihelion passage in September, 1844, might be as long as 2025 days, or it might not exceed 1964 days. Dr. Berberich finds the period of Barnard's comet 1959 days, and Mr. Egbert, of Albany, U.S., 1970 days, so that the periods of the two comets are pretty accordant; but the interval 1844–1884 does not correspond thereto, and the differences that exist in the other elements, notwithstanding the general similarity remarked by Weiss, point to considerable perturbation in this interval, supposing the identity of the comets. De Vico's comet in the orbit of 1844 could not have approached near to the planet Jupiter, to which body we are accustomed to look, as the great disturber of cometary orbits, but there is the possibility of a very close approach to the planet Mars, and this is also the case in a striking degree with Barnard's comet, which, in Dr. Berberich's last ellipse, is less than 0.008 of the earth's mean distance from the orbit of Mars in about 350° 50′ heliocentric longitude; as already pointed out in this column, there may have been a close approach of the two bodies at the end of 1873 or beginning of the following year. The nearest approximation of the orbits of 1844 and 1884 is 0.043 in heliocentric longitude 310°, and there is another approximation, 0.065, in 143°. At present, however, the identity of the comets of De Vico and Barnard is to be regarded as at least doubtful.